当开发者创立了自定义组件,并想对该组件增加特定性能时,例如在自定义组件中增加一个点击跳转操作。若间接在组件内嵌入事件办法,将会导致所有引入该自定义组件的中央均减少了该性能。为解决此问题,ArkUI 引入了 @BuilderParam 装璜器,@BuilderParam 用来装璜指向 @Builder 办法的变量,开发者可在初始化自定义组件时对此属性进行赋值,为自定义组件减少特定的性能。该装璜器用于申明任意 UI 形容的一个元素,相似 slot 占位符。

阐明:

从 API version 9 开始,该装璜器反对在 ArkTS 卡片中应用。

装璜器应用阐明

初始化 @BuilderParam 装璜的办法
@BuildParam 装璜的办法只能被自定义构建函数(@Builder 装璜的办法)初始化。

● 应用所属自定义组件的自定义构建函数或者全局的自定义构建函数,在本地初始化 @BuilderParam。

@Builder function GlobalBuilder0() {}@Componentstruct Child {  @Builder doNothingBuilder() {};  @BuilderParam aBuilder0: () => void = this.doNothingBuilder;  @BuilderParam aBuilder1: () => void = GlobalBuilder0;  build(){}}

● 用父组件自定义构建函数初始化子组件 @BuildParam 装璜的办法。

@Componentstruct Child {  @Builder componentBuilder() {    Text(`Parent builder `)  }  @BuilderParam aBuilder0: () => void = this.componentBuilder;  build() {    Column() {      this.aBuilder0()    }  }}@Entry@Componentstruct Parent {  @Builder componentBuilder() {    Text(`Parent builder `)  }  build() {    Column() {      Child({ aBuilder0: this.componentBuilder })    }  }}

● 需注意 this 指向正确。

以下示例中,Parent 组件在调用 this.componentBuilder()时,this.label 指向其所属组件,即“Parent”。@Builder componentBuilder()传给子组件 @BuilderParam aBuilder0,在 Child 组件中调用 this.aBuilder0()时,this.label 指向在 Child 的 label,即“Child”。对于 @BuilderParam aBuilder1,在将 this.componentBuilder 传给 aBuilder1 时,调用 bind 绑定了 this,因而其 this.label 指向 Parent 的 label。

阐明:

开发者审慎应用 bind 扭转函数调用的上下文,可能会使 this 指向凌乱。

@Componentstruct Child {  @Builder componentBuilder() {    Text(`Child builder `)  }  label: string = `Child`  @BuilderParam aBuilder0: () => void = this.componentBuilder;  @BuilderParam aBuilder1: () => void = this.componentBuilder;  build() {    Column() {      this.aBuilder0()      this.aBuilder1()    }  }}@Entry@Componentstruct Parent {  label: string = `Parent`  @Builder componentBuilder() {    Text(`${this.label}`)  }  build() {    Column() {      this.componentBuilder()      Child({ aBuilder0: this.componentBuilder, aBuilder1: this.componentBuilder })    }  }}

应用场景

参数初始化组件

@BuilderParam 装璜的办法能够是有参数和无参数的两种模式,需与指向的 @Builder 办法类型匹配。@BuilderParam 装璜的办法类型须要和 @Builder 办法类型统一。

class GlobalBuilderParam {  label: string = ""}@Builder function GlobalBuilder1($$ : GlobalBuilderParam) {  Text($$.label)    .width(400)    .height(50)    .backgroundColor(Color.Blue)}@Componentstruct Child {  @Builder componentBuilder() {    Text(`Child builder `)  }  label: string = 'Child'  // 无参数类,指向的componentBuilder也是无参数类型  @BuilderParam aBuilder0: () => void = this.componentBuilder;  // 有参数类型,指向的GlobalBuilder1也是有参数类型的办法  @BuilderParam aBuilder1: ($$ : GlobalBuilderParam) => void = this.componentBuilder;  build() {    Column() {      this.aBuilder0()      this.aBuilder1({label: 'global Builder label' } )    }  }}@Entry@Componentstruct Parent {  label: string = 'Parent'  @Builder componentBuilder() {    Text(`${this.label}`)  }  build() {    Column() {      this.componentBuilder()      Child({ aBuilder0: this.componentBuilder, aBuilder1: GlobalBuilder1 })    }  }}

尾随闭包初始化组件
在自定义组件中应用 @BuilderParam 装璜的属性时也可通过尾随闭包进行初始化。在初始化自定义组件时,组件后紧跟一个大括号“{}”造成尾随闭包场景。

阐明:

此场景下自定义组件内有且仅有一个应用 @BuilderParam 装璜的属性。

开发者能够将尾随闭包内的内容看做 @Builder 装璜的函数传给 @BuilderParam。示例如下:

// xxx.etsclass CustomContainerParam {  header: string = '';}@Componentstruct CustomContainer {  @Builder componentCloser() {    Text(`Custom closer `)  }  @Prop header: string = '';  @BuilderParam closer: () => void = this.componentCloser;  build() {    Column() {      Text(this.header)        .fontSize(30)      this.closer()    }  }}@Builder function specificParam(label1: string, label2: string) {  Column() {    Text(label1)      .fontSize(30)    Text(label2)      .fontSize(30)  }}@Entry@Componentstruct CustomContainerUser {  @State text: string = 'header';  param: CustomContainerParam = {    header: this.text  };  build() {    Column() {      // 创立CustomContainer,在创立CustomContainer时,通过其后紧跟一个大括号“{}”造成尾随闭包      // 作为传递给子组件CustomContainer @BuilderParam closer: () => void的参数      CustomContainer(this.param) {        Column() {          specificParam('testA', 'testB')        }.backgroundColor(Color.Yellow)        .onClick(() => {          this.text = 'changeHeader';        })      }    }  }}